Dirk Franco

Use of thermogravimetric analysis-Fourier transform infrared spectroscopy in the study of the reaction mechanism of the preparation of Pb(Zr, Ti)O3 by the sol-gel method

Abstract The thermal decomposition of a sol-gel precursor of Pb(Zr, Ti)O 3 is studied by thermogravimetric analysis-Fourier transform infrared spectroscopy in argon and in air. It is found that in an inert atmosphere the presence of residual carbon inhibits the formation of the perovskite structure. In air the evolution of volatile compounds such as alcohols, esters, ethers and CO 2 at temperatures above 300°C indicate that polymerization is still going on during the thermal decomposition of the precursor.

Sulphur group analysis in solid matrices by atmospheric pressure-temperature programmed reduction

The atmospheric pressure-temperature programmed reduction (AP-TPR) has become an established and reliable method amongst the different sulphur characterisation techniques for solid materials, like coal and coal derived products, rubber and clay. The analytical method is based upon the fact that specific sulphur functional groups are hydrogenated at specific temperatures. During the last few years, several adjustments have been made to the hard- and software as well as to the experimental parameters. The changes and the reliability of the method are extensively discussed in this paper.

Interaction of the organic matrix with pyrite during pyrolysis of a high-sulfur bituminous coal

Abstract High-sulfur bituminous coal containing 4.17 wt% of pyritic sulfur and the pyrite concentrate separated from this coal were used to examine the interaction between pyritic sulfur and the organic part of coal during pyrolysis. At 330–500°C, as a result of the reaction of sulfur derived from pyrite decomposition with the coal organic matrix, a significant increase in the organic sulfur in the char is observed, from 1.47 to 3.17 wt%. The enrichment in sulfur is most pronounced between 400 and 450°C, corresponding to the most intensive thermal degradation of this coal. At these temperatures, some of the pyrite is converted to pyrrhotite. The organic sulfur content is a maximum at ∼ 500°C, when all the pyrite is reduced to pyrrhotite. The pyrite in the coal undergoes conversion to troilite via pyrrhotite at lower temperatures than does pure pyrite. Compared with the thermal decomposition of pure pyrite, the pyrite present in coal starts to decompose at a lower temperature (330 vs. 400°C). The conversion to troilite also proceeds to completion at a much lower temperature. This demonstrates that the decomposition of pyrite is markedly affected by the presence of the organic coal substance.

Determination of sulfur groups in pyrolysed low-rank coal by atmospheric-pressure t.p.r.

Abstract Atmospheric-pressure temperature-programmed reduction (t.p.r.) was used to follow in pyrolysed sub-bituminous coal the changes in amount of pyrite and in organic sulfur groups as a function of temperature. At higher pyrolysis temperatures, pyrite and aliphatic and mixed aliphatic-aromatic sulfides disappeared systematically and more complex sulfur compounds such as aromatic sulfides and simple thiophenic structures were formed.

Hydrothermal synthesis of ZnO nanorods: a statistical determination of the significant parameters in view of reducing the diameter

In this paper a 2(8-4) fractional factorial design of experiments is applied to identify the important parameters that affect the average diameter of ZnO rods, synthesized by means of a hydrothermal procedure. A water-based Zn(2+) precursor is used for the formation of one-dimensional ZnO particles, without the presence of an organic additive. Results indicate that, at the investigated levels, four of the parameters have a significant effect on the mean diameter. These are the temperature, the heating rate, stirring and an ultrasonic pre-treatment of the precursor solution. Experiments carried out with zinc acetate and zinc chloride do not show a significant difference in rod diameter. Other parameters that do not show a significant effect are the concentration of Zn(2+), the molar ratio between the hydroxyl and the zinc ions, and the reaction time. Interactions are observed between stirring and an ultrasonic pre-treatment and between the zinc concentration and the OH:Zn ratio. By fixing the significant factors at their optimal value it is possible to decrease the mean diameter. The particles are characterized by means of x-ray diffraction (XRD) and transmission electron microscopy (TEM).

Rank dependence of organic sulfur functionalities in coal

Organic sulfur functionalities were characterized and quantified by atmospheric-pressure temperature-programmed reduction (AP-TPR). Nine coals were chosen to cover the entire rank range from subbituminous coal to anthracite. To be able to study the organic sulfur groups, the vitrinite concentrates were separated from each coal sample. The results confirm the larger amount of sulfide in low-rank coals. The amount of thiophenes generally increases with rank. Nevertheless, sulfur functionality distribution can vary from coal to coal even at the same rank.

Effect of calcium and calcium minerals in coal on its thermal analysis

Abstract The effect of the presence of limestone and dolomite in coal, and calcium in lignite, on atmospheric-pressure temperature-programmed reduction (AP-TPR) analysis was studied. AP-TPR experiments were carried out on a bituminous coal with added limestone and dolomite and on a demineralized lignite. The results showed that both calcium minerals captured the gaseous H 2 S formed under AP-TPR conditions and produced CaS. Consequently the sulfur recovery monitored was too low and the AP-TPR kinetograms were deformed. The study also showed that the influence of dolomite is greater than of limestone. AP-TPR analysis of lignite demineralized and then loaded with calcium ions again showed a clear lowering of sulfur comparable with that of dolomite, but starting at a higher temperature.

The decomposition of the oxalate precursor and the stability and reduction of the YBa2Cu4O8 superconductor studied by TG coupled with FTIR and by XRD

The 124 superconductor YBa2Cu4O8 was prepared from the oxalate precursor Y2(C2O4)3. ·4BaC2O4·8CuC2O4·xH2O at one atmosphere oxygen pressure. In O2 the precursor decomposes in one step at 300°C and more gradually (300°–600°C) in Ar. The stability of the superconductor is strongly dependent on the gas atmosphere: in O2 and in air there is no significant weight change as long as the temperature does not exceed 800°C, whereas in a 1% O2-99%N2 mixture decomposition starts at about 670°C with the formation of CuO and YBa2Cu3Ox withx<7. The reduction of YBa2Cu4O8 in a 5% H2-95% Ar mixture takes place in at least four major steps with formation of products such as Y2O3, BaO, Cu2O, Cu, BaY2O4 and Ba4Y2O7.ZusammenfassungAus dem Oxalatpräkursor Y2(C2O4)34BaC2O48CuC2O4·xH2O wurde der 124 Supraleiter YBa2Cu4O8 hergestellt. In Sauerstoff zersetzt sich der Präkursor bei 300°C in einem Schritt, in Argon nach und nach (300°–600°C). Die Stabilität des Supraleiters hängt stark von der Atmosphärenzusammensetzung ab: in Sauerstoff und in Luft gibt es bis 800C keinen bemerkenswerten Gewichtsverdust, während in einem Gemisch aus 1% O2 und 99% N2 die Zersetzung bei etwa 670°C beignnt, wobei CuO und YBa2Cu3Ox mitx gebildet wird. Die Reduktion von YBa2Cu4O8 in einem 5%H2-95%Ar-Gemisch erfolgt in mindestens vier Hauptschritten, wobei Produkte wie Y2O3, BaO, Cu2O, Cu, BaY2O4 und Ba4Y2O7 gebildet werden.

Sulphur distribution in Illinois no. 6 coal subjected to different oxidation pre-treatments

Abstract The effect of different oxidation pre-treatments on the sulphur distribution in Illinois No. 6 coal (IBC-101) was studied using Atmospheric Pressure-Temperature Programmed Reduction (AP-TPR). Oxidation pre-treatments were carried out on demineralized coal with peroxyacetic acid (PAA) as a function of reaction time. For the longest reaction time the effect of PAA on the coal was compared to the effect of several other oxidants. AP-TPR results also show a clear effect of LiAlH 4 on the coal. Not only is pyrite removed, but there is also a decrease in other sulphur forms. Subsequent PAA oxidation causes an overall decrease of the AP-TPR signal, signifying the attack on organic as well as inorganic sulphur forms. With other oxidants, under the same conditions, only minor differences could be found after different treatments.

A.p.–t.p.r. investigation of the effect of nitric acid leaching on the sulphur distribution in coal

Abstract The effect of nitric acid leaching on the sulphur distribution in Emma and Mequinenza coal was studied here, as previous work demonstrated that nitric acid was able to remove more than just inorganic sulphur under certain experimental conditions. In contrast with standard methods, in which nitric acid is used to remove pyritic sulphur, atmospheric pressure–temperature programmed reduction (a.p.–t.p.r.) was used to specify which organic sulphur functionalities are easily removed by nitric acid treatment, and which are more difficult to remove.